By means of protoplast fusion and genetic transformation, the relationship of the known linkage groups to the entire chromosome of Staphylococcus aureus is to be investigated. Many regions of the chromosome have been identified as insertion sites of the transposon Tn551(Em) and some of these sites are thus far in undefined regions of the chromosome. A mechanism of analysis of protoplast fusion-generated recombinants is to be used that allows one to define a donor and a recipient, and analyze the recombinants accordingly. A second aspect of these studies involves the transfer (probably by protoplast fusion) of plasmids from Streptococcus faecalis to Staphylococcus aureus. The primary purposes for this are (1) two of these plasmids bear new Tn elements which should be invaluable for further genomic mapping by defining their insertion sites and (2) two other plasmids are conjugative in Streptococcus, are known to be transferrable to staphylococci by conjugation, and are of interest as a means of conjugal analysis within Staphylococcus aureus.